o-Tolidine is useful in preparing polyurethanes, epoxies, polyamides, and polyimides and is the source of several property enhancements for these systems. However, its properties also create a number of processing problems. For example, it has a high melting point (130.degree. C.) and this precludes its use as a RIM (Reaction Injection Molding) chain extender in polyurethanes. This high melting point complicates its use as an epoxy curative. The high amine reactivity complicates processing. Another complicating factor is that amine reactivity is not differential and many applications may require moderation to control cure profiles. Lastly, o-tolidine is an animal carcinogen and that fact also detracts considerably from its attractiveness in many applications.
Alkylation of a variety of aromatic amines has been reported to alter properties, e.g., amine reactivity. Typically alkylated amines are formed by contacting the aromatic amines with a hydrocarbon radical-providing source such as an olefin or alcohol. Such alkylation methods are widely known. Reference is made to the following patents which are representative of the processes for the alkylation of aromatic amines:
Stroh, et al. in U.S. Pat. Nos. 3,275,690; 2,762,845; West German AS 1051,271 and Japanese 38-4569 disclose various processes for the manufacture of alkylated aromatic amines by effecting reaction between an aromatic amine and an olefin. Representative aromatic amines for alkylation include primary amines, such as, aniline, toluidines, xylidines; secondary amines such as diphenylamine and diamines such as m-phenylenediamine and various toluenediamine isomers. In the '690 patent, various Friedel-Crafts catalysts such as aluminum chloride, zinc chloride, boron fluoride and other halogen compounds are combined with aluminum to effect the catalytic reaction. In the '845 patent, aluminum powder is used as a component of the catalyst system. The West German '271 patent uses various bleaching earths and montmorillonite as the catalyst.
British patent 846,226 and U.S. Pat. Nos. 2,115,884; 4,351,958; 4,446,329; and 4,740,620 show the use of heterogeneous catalysts in the alkylation of aromatic amines. The '884 patent discloses the ring alkylation of aromatic hydrocarbons using activated hydrosilicates and hydrated silicic acids, commonly referred to as bleaching earths. The '958 patent discloses iron oxides as catalysts for such alkylation and the '329 patent discloses the use of a metal cation salt of a perfluorosulfonic acid polymer, the polymer typically being sold under the trademark Nafion.RTM.. The '620 patent discloses the reaction of aromatic amines with olefins in the presence of acidic crystalline alumino-silicates to produce the alkylated counterparts thereof.
U.S. Pat. Nos. 4,740,620; 4,745,223; and 4,760,184 disclose alkylation of aromatic amines by reaction with olefins in the presence of highly acidic zeolites. Mononuclear and bridged amines are suggested as candidates for alkylation.
U.S. Pat. No. 4,482,690 discloses the curing of polyurethane/urea elastomers using alkylated aromatic amines. The '690 patent discloses the use of tert-butyl-m-phenylenediamine as a chain extending agent. Delayed reactivity of the substituted aromatic amine is noted as an advantage.
U.S. Pat. Nos. 3,428,610 and 4,218,543 note the use of mono and diethyltoluenediamine as delayed action chain extenders for polyurethane/urea elastomers.
U.S. Pat. No. 4,482,690 discloses the use of tert-butyl-toluenediamines as delayed action chain extenders for polyurethane/urea elastomers. The mono-tert-butyl-2,6-toluenediamine was noted as having excellent delayed reaction characteristics.